Coaxial line type impulse generator with centering means for coaxial conductor



April 12, 1960 J. LORCH 2,932,802

COAXIAL LINE TYPE IMPULSE GENERATOR WITH CENTERING MEANS FOR COAXIAL CONDUCTOR Filed Dec. 28, 1956 s Sheets-Sheet 1 '3 \W Win44;

IN V EN TOR.

7 BY W J0 April 12, 1960 MEIA OR COAXIA ONDUCTO 3 Sheets-Sheet 2 Filed Dec. 28,

ORCH ,932,802 AXIAL LINE TYP MPULSE GE ATOR w NTERING April 12, 1960 J. LORCH 2,932,802 COAX LINE TYPE IMPULSE ERATOR WITH CEN ING MEANS FOR COAXI. CONDUCTOR Filed Dec. 28, 1956 3 Sheets-Sheet s WNW United States Patent Joseph Lorch, West Hemp stead, N.Y., assignor to Empire Devices, Inc., Bayside, N.Y.

Application December 28, 1956, Serial No. 631,363 20 Claims. (Cl. 331-127) This invention relates to impulse generators, and more particularly relates to improved impulse generator ad-. justing mechanism for the unit to obtain optimum output and maintain such optimum output over a relatively long period.

An impulse generator is designed with a capability of producing periodic pulses of such shape and duration that they contain energy components from the repetition rate frequency to the order of a high microwave frequency, such as 40 kilomegacycles. The pulses are produced by discharging a small length of charged lossless coaxial transmission line into a resistance through a mechanically vibrating contact. By proper choice of transmission line impedances, it is possible to produce periodic transients having a uniform frequency spectrum out to a predetermined high frequency. This is accomplished by applying a step voltage through a lumped resistance to the coaxial transmission line. US. Patent No. 2,722,608 is an example of such impulse generator.

The ratio of the impedance of the charged lossless coaxial transmission line referred to, to that of the output transmission line, determines the nature of the decaying pulses. This ratio is the criteria for determining the output energy at its spectral or frequency distribution. A satisfactory impulse generator has such ratio maintained substantially constant. Towards this end, the supporting member for the charging resistance and the central charged coaxial line must be maintained precisely concentric with respect to its outer line conductor. Otherwise variations in concentricity would produce non-uniformity in the respective decaying pulses, particularly at the high spectrum end. The concentricity of the charged line within its outer conductor must be far better than 0.5 thousandths of an inch, which is the best mechanical positioning heretofore possible in such units, to uniformly extend to high microwave frequencies 50 It is the primary purpose of the present invention to provide a novel impulse generator structure and arrangement which is readily centered when assembled; where such centering or coaxial alignment of the charging line with its outer conductor is detectable by the assembler; and which assembly remains centered safely during extended normal operational use of the impulse generator. The centering accuracy is such to maintain uniform results, without the prior art difliculty of even minute eccentricity causing unsteady and uneven results. 50

The impulse generator transducer of the present invention is mountable in a cylindrical member which contains the outer conductor for the charged line, and the output coaxial transmission line extending therefrom. The mechanical impulse generator transducer has a flange which is locked by a clamping ring coacting with the cylinder, after precise coaxial centering. A pair of spring loaded set-screws are arranged about the transducer, resting within the aforesaid cylindrical member in substantially 90 relation. An additional pair of set-screws are 70 arranged at diametrically opposite positions with respect to the spring loaded set-screws. By a simple procedure,

2,932,802 Patented Apr. 1 1 0.

the transducer head is precisely positioned with the charged line precisely concentric within the coaxial outer conductor. Further means are provided to lock the setscrews in the adjusted position. The clamping ring locks the transducer within the cylindrical sleeve to maintain the impulse generator as a rigid assembly, with consistent and accurate electrical performance.

It is accordingly an object of the present invention to provide a novel impulse generator with precise centering means for the charging line thereof.

A further object of the present invention is to provide a novel centering means for an impulse generator transducer, wherein the charging line is precisely centered and maintained coaxial with its outer conductor.

Another object of the present invention isto provide an impulse generator centering system embodying a plu-' rality of spring loaded and companion set-screws.

Another object of the present invention is to provide an impulse generator having means for precisely centering the charging line elements thereof, and for maintaim ing such precise adjustment for extended operating periods.

These and further objects of the present invention will become more apparent in the following description of an exemplary embodiment thereof, taken in connection with the following drawings, in which:

Fig. l is a diagrammatic illustration of generator system.

a basic impulse Fig. 2 is a schematic showing of the impulse generator structure used with the present invention.

Fig. 3 is a perspective illustration of the transducer unit of the invention impulse generator.

Fig. 4 is a longitudinal cross-sectional view through the transducer centering and securing structure of the present invention.

Fig. 5 is an enlarged cross-sectional view through the charging transmission line of the impulse generator, taken along the line 55 in Fig. 4.

Fig. 6 is a horizontal sectional view, along the line 6-6 of Fig. 4 in the direction of the arrows, used for explaining the centering of the impulse generator in the invention system. (The eccentricity of the respective sections of the Fig. 6 generator being exaggerated for descriptive purposes.)

Fig. 7 is an enlarged cross-sectional view through the line 7-7 of Fig. 6, illustrating the spring loaded set-screw of the invention adjusting system. i

Fig. 8 is an end view of the set-screw head, as seen at line 88 of Fig. 7.

Fig. 9 is an enlarged cross-sectional view taken along the line 99 of Fig. 6, through the fixed set-screw section of the invention adjusting system.

Fig. 10 is an end view of the fixed set-screw of Fig. 9, as seen at line 10-10 thereof.

Figs. 11 and 12 are diagrams used in connection with the exposition of the method and system for centering the impulse generator coaxial line in the invention system.

Fig. 1 is a simplified diagram of an electrical impulse generator. The small length lossless coaxial transmission ine 15 is charged through an adjustable voltage E and charging resistorR The charged transmission line 15 is coextensive with output transmission line 20. The output transmission line contains outer cylindrical conductor 21 and coaxial inner conductor 22 centered and spaced from outer conductor 21 with a suitable low-loss insulation cylinder 23. The output transmission line 20 may be gradually tapered until its output coupling is of a standard physical size. In this manner the eifective impedance of the transmission line is predetermined at its juxtaposition and connection R with the output of charging coaxial line 15. When the output (not shown) of the I The output conductor 16 is travel the length of the transmission line.

- train'is about 350 micromicroseconds.

- output transmission line 20 is properly terminated to a in the circuital analysis of the impulse generator action,-

aswjll be set forth.

'The charging coaxial transmission line comprises a conductive sleeve or cylinder 16, and a central longitudinally displaceable contact plunger 17. Contact plunger 17 in the exemplary embodiment, is of silver. Its free end 18 is arranged to contact the fixed central contact point 19 of the central conductor 22 of output line 20. connected to ground, as is one side of the D.C. supply E The left end 24 of vibratory plunger 17 is suitably secured to the center of a vibratory diaphragm 25. The charging resistor R is connected between the battery E and central point 24. The diaphragm 25 is insulatingly supportedby the schematically indicated flanges or end members 26, 26. Thus voltageis impressed upon vibratory contact plunger 17 through charging resistance R by the adjustable voltage soure E Diaphragm 25 is insulated with respectto ground potential, and the charge on plunger 17 is established with respect to grounded conductor 16 of the short coaxial cable 15. r

Forthe purposes of analysis, the generator may be considered an initially charged uniform transmission line of characteristic impedance Z to whicha charging voltage e was applied through a resistance R The transient produced is a pulse train with an overall time duration extremely short compared with the time necessary to When the ratio of the load termination R to the characteristic impedance 2 of the transmission line is properly chosen, thespectrum of the pulse train will be essentially flat to 'a frequency approximately equal to the resonant frequency of the charged transmission line 15. The resulting pulse train will decay exponentially as a function of the reflection coefiicient.

For an impulse generator whose resonant frequency is; for example, about 10 kmc., the individual pulse in the train with a width of about 50 microicr oseconds (5 1O'" seconds), and the effective time duration of the wave With a reflection coefiicient of -.17 l7, a reasonably fiat spectrum is obtained up to a frequency of 0.9 f onant frequency of the transmission line). If a highly selective circuit is excited by a voltage impulse, the voltage output oscillates at the resonant frequency of the selective circuit. The envelope of the RF oscillation de cays in time as a function of the bandwidth of the tuned circuit, and the peak envelope voltage is proportional to the peak impulse input voltage to the tuned circuit;

The magnitude of the voltage spectrum of a generator A( in microvolts/megacycle of bandwidth depends,

' for reasons already mentioned, entirely on the'geometry and DC. charging potential e of the impulse generator.-

The spectral intensity in microvolts/megacycle is defined (where his the res r may air.

for practical purposes as follows: It is equal to the num ber of R.M.S. sine wave rnicrovolts (unmodulated) applied to the input of the measuring device as its center frequency, which will result in a maximum response at the output equal to that resulting from the pulse being measured, divided by the effective impulse bandwidth of the circuit in megacycles.

The spectrum of an impulse, from the purely mathe matical standpoint is considered to extend as far into the negative frequency domain as into the positive, and a physical bandpass filter or amplifier to which the spectrum is applied responds as if it were receiving not only the energy in its actual passband but also that in the corresponding negative frequency band.

Let A( represent the magnitude of the mathematical voltage spectrum in v./cycle/sec., and S the effective spectral intensity in v./cycle/D.C. charging'voltage on thetransmission line, the discharge of which generates the impulse. Then:

. 2A(j) T, p I

where e is the DC. voltage to which the line is'charged. The power output from a filter with a rando'm noise bandwidth BW(n), produced by an impulse generator at its input,-is given by the following relation:

' 6 8 0 fr' R mnx' P =Output power in watts of the filter assuming output in volts/cycle/ I There the interference generators calibration is in N DB above one microvolt/meg'acycle, with reference to e, as supplied to a 50 ohm load, the following" holds:

uV R.M.S./rne.=e-f=l0g,( Substitution of a into '1 gives:

The use of the interference generator for noise figure measurements is based on this formula.

Fig. 2 is a schematic drawing of the exemplary impulse generator utilized in the invention system. The output transmission line 30 comprises a cylindrical outer con= ductor 31; Conductor 31 is threaded at its external surface 32 for mounting within a cylindrical ho'using, to be described in connection withFig. 4. The central inner coaxial conductorf 33 is secured within the cylindrical conductor 31 through a suitable central bushing 34 of low-loss dielectric material such as Teflon. Teflon is a registered trademark of insulation material made of t'etrofluo'rethylene. However, other equivalent insulation'for the transmission line conductors may be used, as

The short charging coaxial transmission line 35 corresfonds to the diagrammatic line 15 of Fig. 1. The di electric material between central vibratory contact or plunger 36 and exterior conducto'r 31a, is air. It is to be noted that the outer conductor for contact 36 is simply an extension of cylindrical tube 31 of the output transmission line 30," and is integral therewith. The vibratory contact 36 is arranged coaxially with and electrically engageable with contactor 37. Contact 37 is integral with central conductor 33 of output transmission line 30.

The body of vibratory plunger or contact 36 is of silver. It is made integrally coextensive with charging resistor R, indicated at 38. The resistor R is secured to the central portion 39 of the vibratory diaphragm 40. In the exemplary embodiment, charging resistor 38 is 200 megohms, and of course may be of an equivalent 7 a high resistance value in this range. The charging voltage e is applied to terminal 41 connected to the central portion 39 of diaphragm 40, and in turn to charging resistor 38 and silver contact-plunger '36. r "T he charging voltage resultant at terminal 41 .i eq ivalent to. a predetermined adjustment of the DC. voltage E indicated, in Fig. I, and is'applied directly to the charging resistance R which is element 38 in Fig.

. The vibratory diaphragm 40 is preferably circular and mounted in a suitable insulation retainer ring 42 such as of fLucite. The exemplary diaphragm 40 is made of Invar, and is .002 inch thick. The diaphragm 40 is arranged to vibrate through suitable electromechanical means. It is noted that diaphragm 40 is well insulated from the remainder of the transducer, transmission lines, and other electrical elements of the system through the substantial insulation retainer ring 42 within which it is mounted. The extent of vibration of the exemplary contact 36 is up to .020 inch. In other words the gap existing between contact plunger 36 and contact 37 is of the order of .020 inch or less in the exemplary design.

The rate of vibration of diaphragm 40 is controlled by' a sinusoidal trigger frequency introduced to the terzrninals 43 of electromagnet 44 of the transducer unit, :indicated generally at 45 in Fig. 2 (see also Fig. 3). The rate of vibration or triggering in a practical and an exremplary unit extends from about 25 to 3000 cycles. The transducer 45 is a relatively simple unit, functioning simi- 'larto some types of telephone receiver units. It consists basically of a metallic iron flap placed between the poles of permanent magnets (not shown). Around the flap is found a coil which is excited by a suitable voltage (sinusbidaL-square or pulse), causing the ends of the flap to assume magnetic poles depending upon the direction of current flow through the coil. Thus the flap is caused to vibrate back and forth between the magnets. The contacts of the generator are connected to this fiap by means of a Bakelite rod and Such electromechanical means is schematically indicated at 44 in Fig. 2, and is contained within the cylindrical enclosure 46 of transducer 45 (see Fig. 3). Details of such transducer construction are shown in the art, and are not detailed herein. 1

In the exemplary impulse generator unit, the characteristic impedance of the charging short coaxial trans mission line 35 is 20.5 ohms. The diameter of the vibratory contact 36 is made the same as that of the central conductor 33 of output transmission line 30. Accordingly their common outer cylindrical conductor 31 produces the same inside diameter-for the outer electrical portion of the two lines 30, 35. The insulation section between the output transmission conductors 31 and 33, preferably of Teflon, which is the dielectric filling for the output transmission line, is proportioned to make its characteristic impedance 14.1 ohms. Also in the exemplary units, the longitudinal dimension of the vibratory plunger 36, namely the silver conductor section extending from the charging resistor 38,-is 0.187 inch.

The described impulse generator has been found to provide excellent output, with a fiat frequency characteristic from 20 kilocycles up to 40 kilomegacycles. Such flat frequency response and extent of spectrum is importantly due to the precisely centering of contact 36 with respect to the fixed contact 37 and within circular outer conductor 31a. The ratio of the impedances of the input at line 35 is important with respect to the flatness of the spectral output, and the extent of its frequency range. A very' smalleccentricity of the contact or vibratory plunger 36 within and fixed cylindrical outer conductor 31a distorts the impedance relationships and disturbs the optimum flatness of range of the spectral output of the impulse generator. It is an important objective of the present invention to provide for precise central positioning of vibratory plunger 36 with respect to its outer conductor 31a, and to maintain such precise concentricity during extended operating conditions of the unit.

' It is to be noted that the proportions and dimensions of therespective elements and component'sof the impulse generator system, as shown in Fig. 2 and other figures,

m intentionally not to scale in order to more-"clearly a supported diaphragm.

illustrate and define their; features and relationships. It is to be also understood that the invention system, as is further described hereinafter, is applicable to impulse generators of other constructions, and with different parameters and ranges thanthe exemplary unit described herein for illustrative purposes.

Fig. 3 shows a transducer unit 45 in perspective, which corresponds to the portion of Fig. 2 including central vibratory plunger 36 and all elements illustrated to the left thereof, including the charging resistor 38, vibratory diaphragm 40, and the electromechanical means 44 for controllable vibrating diaphragm 40. The transducer 45 is of cylindrical shape and contains outer enclosure 46 within 'which the electromechanical vibratory means (corresponding to 44 Fig. 2) is housed. Electrical plug connectors 47, 48, 49 extend from the rear of transducer 45, forsuitable electrical connection to the circuit elements therewithin, as will now be understood.

- The vibratory diaphragm 40 is seen supported within a thick cylindrical member 42 of Lucite or equivalent insulation material. The charging resistor 38 and contactor 36 extend centrally beyond the plane face at the right end of transducer 45. The transducer 45 is secured to the .houshing of the output transmission line (as is described in connection with Fig. 4), through extending flange 50 and sleeve 51. The transducer unit 45 is essentially a unit for extending charging resistor 38 and contact 36 from vibratory diaphragm 40, and controllably vielectromechanical means within the enclosure 46. The electrical charging voltage e is fed to charging resistor 38 and contact 36 through a rear connector, and in the manner already described in con nection with Figs. 1 and 2.

Fig. 4 illustrates the transducer 45 assembled with output transmission line 30 by means of solid housing 52. Housing 52 is cylindrical and preferably made of aluminum. The central upper portion of housing 52 is suitably threaded to receive outer conductor 31 threaded at 32. The central portion of housing 52 is made hollow to receive the head 51 of transducer 45. The head-sleeve portion 51 of transducer 45 is parallel to and projects adjacent to the bottom surface 53 of the hollow. The cylindrical flange 50 of transducer 45 rests in undercut 54 of 52. The dimensions of transducer 45 including sleeve 51 and flange 50, and that of housing 52 including its central recess portion 53, the location of the charging dercut or recessed portiton 54, all arrangement as shown in Fig. 4.

The transducer contact 36 is in the axial position of the housing, and concentric with center conductor 33 of 30. A retaining ring 55 is ar- 0 hold the transducer 45 in housing 52 through threaded section 56. Initially the clamping ring 55 is ing of the transducer contact 36 is accomplished in a manner hereinafter described. Ring 55 is thereupon turned to press further against flange 52 and assist the set-screws in holding the assembly of the transducer 45 andhousing 52 intact after the final precise centering adjustment.

' Fig. 5 is an enlarged cross-sectional view along the line 5-5 through the short charging transmission line 35, The central concentric tory plunger 36, mission line 35, and is centrally of outer conductor 31 within the housing 52. A slight displacement of central contact 36 with respect to the inner cylindrical surf-ace 57 of outer conductor 31 causes non-uniform spectral an adjusting set-screw 61 housing 52. The portion of four set-screw assemblies 'gssasoir outer conductor 3-1 at are cha ging: coaxial transit-inside H9935. I r L' .f f Fig. 6 is a cross se'ctional view through the transducer entering and securing means,- taken along the line 6==6 of Fig. 4. The transducer is indicated centrally at 45 with its eccentric position drawn exaggerated for pur pdses of illustration. The transducer contact 36is centrally. of and projects axially from the transducer '45. The projectir'ig-sleeve 51 at the bottom of transducer 45 coaets with two pairs of adjustable mounted set-screws asfollow's: Spring loaded set-screw assembly 60,. with diametrically opposite thereto;- and spring loaded set-screw arrangement 62, oriented 90 from set-screw assembly 60, with an adjustable set-screw 63 diametrically opposite thereto.

'Fig. 7 is an enlarged cross-sectional view through As shown in Figs. 9 and assembly 61 is composed of sleeve 80 threaded and'se cured at 81 into housing 52. The internal bore of sleev 80 is threaded at 82 toreceive threadedset sc'rew 83.

n Set-screw 83 has a slot 841at its head for longitudinal ad 7 tion by a locking screw 86 fitting within the unused bore the set-screw assembly 62 taken along the line 7--7 of Fig.6; and Fig. 8 is an end view thereof. Fig. 9 is an enlargedcross-sectional view throughthe adjusting setscrew 61 as taken along the line 9--9 of Fig. 6; andFig. 10 is an end view thereof. The spring loading andadjusting set-screw assemblies, corresponding to Figs. 7 and 9 respectively, will first be described in detail, and their operation in conjunction with the plunger 36 center ing, and the fastening of the-transducer, will be thereupon described' in connection with Figs. 6, 11 and 12.

The spring loaded set-screw 62 is identical to that of set-screw assembly 60. As shown in Fig. 7, these cornprise a screw unit 65 having a head 66, an internally axially threaded opening 67, an externally central threaded'section 68, and an extending end rod section 69. The rod section 69 is of the narrowest diameter, and a tension spring 70 is coiled thereabout and extends bee yond rod 69. The central section of screw rnernberj65 is of intermediate diameter, and is threaded within housing body 52. The external head 66 of screw member 65 is hexagonal, and is used to turn the screw member 65 into cylindrical rod end portion mit the helical tension spring 70 which surrounds the rod 69. Thus, a channel is formed for spring 70 between the smooth end rod portion 69, with the channel 71 surrounding it. A set-screw 72 operates within the central threaded bore 67 of screw member 65, and when sufficiently turned by a screwdriver through slotted head 73, has its front end portion 75 abut sleeve 51 of transducer 45. As will be set forth, in the initial stages of adjustment, set-screw 72 is retracted within bore 67 so that its front end 75 does not contact the transducer sleeve 51. During such condition, the tension spring 70 presses against transducer'sleeve 51, and establishes a spring loading contact in tension on'the transducer sleeve for the purpose to be detailed.

When the transducer 45 is accurately centered, it is held by a four-contact assembly including the two springs 70, 70 of the screw assemblies 60, 62. Their set-Screws 72 are thereupon operated to press firmly against the transducer sleeve 51, and thereby establish a positive four-point engagement of the circular sleeve 51 by the p 60 to 63. When the set-screw 72 of each of the assemblies 60 and 62 are thus suitably engaged as aforesaid, it is preferred to have an additional set-screw 76 mounted within the central bore 67 to abut the head .73 of each set-screw 72 therein, and lock the set-screws in position.

In this manner the combination of the spring tension 70, the engaged set-screw 72, as well as the locking setscrew 76, allcombine to firmly hold the sleeve 51 at the identical point contact established for it in connection with the centering procedure to be described in connection with Figs. 6, l1 and 12. Fig. 8 illustrates the head 66 of the set-screw asembly 62, as an integral part of the set-screw member 65. The locking set-screw 76 is Y wa time th e e i -l I housing 52 surrounding the- 69 is undercut at 71 to ad portion 82. The adjusting set-screw 63, oriented from set-screw 61, is identical in construction thereto, and for clarity the identical numerals are used for its components.

' Since the spectral output of the impulse generator depends upon the impedance characteristics of the discharge and output lines, it is most important that the vibrating contact 36, which is the center conductor of the discharge. line, be absolutely centered within the transmission line 35 as hereinabove 'set forth. 'Even slight. eccentricity of the contact 36 with respect to the cylindrical outer conductor surface 57 (see Fig. 5) produces disturbance of the flatness of the generator output frequency characteristic, changes the reflection coefiicient of the impulse generator circuit, and afiects the spectral frequency output thereof. r 7

Before aligning the center contact 36, the discharge resistor of the circuit is removed, and the plunger-contact 36 is, by well known procedure suitably adjusted for optimum axial contact performance to avoid bouncing or contact arcing. In other words the contact 36 should vibrate stably without bouncing'or arcing throughout the repetition frequency range, pg. 25 to 3,000 cycles per second in the exemplary system. Plunger-contact 36 is thereupon concentrically centered as a final procedure for the impulse generator, in the following manner:

(1) The transducer 45is set into the generator housing 52 so that the contact 36 falls into the transmission line 35, butshort of touching the output lines center conductor 37. This condition can be checked by connecting a megohmeter between the charging voltage terminal (41') of the transducer 45 and the center conductor 33 of the output line 30. If the contact 36 touches the center conductor 37, the meter would read the charging resistance (200 megohms). The transducers locking ring 55 is screwed into place so that it holds the transducer 45 firmly, yet not so tight as to prevent side motion during the alignment procedure.

(2) The two adjusting set-screws 61, 63 are set into the housing '52 and advanced just enough to separate the transducers bearing surface 51 from the housing at points where the screws '83 are inserted (see Fig. 9), The purpose for this step is to insure that the insertion of the spring loaded screws 60, 62 will not push the transducer 45 .so far to one side as to cause breakage of the contact 36. I I I (3) The two spring loaded screws 60, 62 are then inserted. These screws are illustrated in Fig. 7. The threaded hole 67 whichfruns through the screws center is also seen in Fig. 7. The purpose of this is for the insertion of locking set-screw 72 which fixes the position of the transducer 45 within the housing 52 after the completion of the aligning procedure. In this step (3) the locking set-screws 72 are not engaged with the transducer sleeve 51, but the springs 70 instead engage this sleeve. 7

(4) The above step (n)fixes the transducer 45 be tween four bearing points. Two of these result from the setting set-screws .83, and diametrically opposite are those'induccd by the tension springs 70. It should now bepossible to move the (90 apart) and cause the transducer contact 36to touch to, the adjusting set scr'ew transducer 45 in two directions the inner'wall 57 of the transmission line 30 at four points. Such contacting isindicated by connecting the megohmmeter between the housing 52 and the charging voltage terminal e of the transducer 45. The setting screws should be turned in and out with a wrench to insure that contact is made at all four points before the adjusting tool is used. (Such adjusting. tool is simply one that translates axial movement of the setting screws (and therefore movement of transducer 45 in the same direction) into angular degree-type readings. Fig. 12 shows the graduated circular dial 90 with arbitrary graduations 91 thereon. The adjusting tool has a head like a screw driver which engages the slots 84 of the adjusting set-screws 83. Axial displacement of screws thetool driver is indicated by corresponding angular positions of indicator 92 on dial 90.)-

Referring to Fig. 11, assume that the position of the contact 36 within the transmission line 35 is such that the contact is at an arbitrary position (1). Assume also that the adjusting set-screws 83 are at points A and B, while the tension springs 70 return the pressure from C and D. By means of the adjusting tool, a setscrew 83 is then turned (either of the two). Let us say'that the set-screw 83 at B is turned, pushing the contact 36 towards point D. This is continued until contact is just made at D, as indicated by the megohmmeter, at which time the indicated angle D on the tools dial 90 noted. The screw is then withdrawn until contact is just made at B. Again the angle for B is noted. The tool is then turned until the pointer indicates an angle exactly half-Way on the arc traveled between B to D contacting points (see Fig. 12). The letters and numbers "in Fig. 12 correspond to positions indicated in Fig. '11;

(6) Step (5) is repeated for the other set-screw 83 at A. This time the contact 36 moves from position (2) towards C, at which time the. angle is noted on tool scale 90. Set-screw 83 is turned to again move back contact 36 to A, where the angle is again noted; and finally to position (3). Position (3) is that resulting by turning with the tool until the angle read on the tool scale 90, is exactly half of that between A and C. Position 3) is the exact center of the transmission line when the alignment is performed carefully.

(7) The locking set-screws 72 are then inserted into the spring-loaded screws 60, 62 until their ends 75 are tight against the transducer 45 (see Fig. 7). Over these locking set-screws 72 are inserted safety set-screws 76, to doubly insure that they will not loosen. This safety locking is also done to set-screws 83 by safety setscrews 86.

In the exemplary embodiment the inside diameter of the surface 57 of outer conductor 31 is .080 inch; the corresponding diameter of the center conductor or contact 36, .062 inch. The spacing between the surface of contact 36 and inner surface 57 is accordingly .010 inch when the concentricity is exact. The impedance of the charging line 35, when the contact 36 is centered within cylindrical surface 57 is 20.5 ohms, resistive. accurate concentricity of contact 36 within cylinder 57, the spectral frequency range is as high as the design of the unit dictates, namely to 40 kmc. Also the spectrum is fiat in that the reflection coefiicient was set at the optimium value of -.1717.

Eccentricity even of the order of one ten-thousandths of an inch affects the value of the reflection coeflicient, and also the spectral content of the output of the impulse generator. The use of the invention centering arrangement permits the contact 36 to be set to an extreme degree of precision, and to maintain such setting under :all normal operating conditions. Thus the invention impulse generator is designed for and maintains a flat frequency spectrum, even when made in production quantities, as the adjustments described hereinabove for centering the contact are done individually as a final to different designs or constructions of, or parameters for the impulse generators. Essentially the invention 7 system establishes the centering of the vibratory plungercontact 36 Within the short charging lossless coaxial line 35, to a precision heretofore unattainable and is arranged to lock such precise setting to insure the high range flat frequency spectrums desirable for impulse generators.

Although the present invention has been described with respect to an exemplary embodiment thereof, it is to be understood that modifications and variations may be made whichare within the full intended scope of the invention as set forth in the following claims.

a I claim:

1. An impulse generator of the character described comprising a transducer unit having a projecting vibratory Contact, a transmission line with a central conductor and an outer conductor coaxial therewith, a housing supporting said transmission line with a portion receiving ing the said precisely set coaxial relationship.

4. An impulse generator of the character described and having a recessed portion to receive said one transducer enclosure end with said contact extending towards said central conductor and said flange engaging said housing, and adjusting means mounted with said housing adjacent said one transducer enclosure end for trans-- recessed portion spectral output of extended acameoa versely positioning precisely said transducer unit in said with said'contactiinto substantially pre'-' ci'se' coaxial relation with said outer conductorinnef surface, and locking means connected with said positioniad'" justing means for maintaining the said precisely set coaxial relation, whereby optimum operation of the um I pulse generator is provided with a substantially flat I frequency range;

5. The impulse generator of claim 1, in which said position adjusting means includes a resilient member, and an adjustable element located diametrically opposite said member. r

6.- The. impulse generator of claim 2, in which said position adjusting means includes a resilient member pressed against said one enclosure end, and anadjustable element located diametrically opposite said member and operable on said one enclosure end.

7. The impulse generator position adjusting means includes a first resilient member pressed against said one enclosure end, a first adjustable element located diametrically opposite said first member, a second resilient member located substantially 90 from said first resilient member and pressed against said one enclosure end, and a second adjustable element located diametrically opposite said second member, said adjustable elements coacting to hold said enclosure and transducer unit in position. v g

'8; The impulse generator of claim 4, in which said position adjusting meansincludes a first resilient member pressed against said one enclosure end, a first ad justable element located diametrically opposite said first member and-operable on said one enclosure end, a second: resilient member located substantially 90 fromsaid firstresilient member and pressed against said one enclosure end substantially in the plane first element, and a second adjustable element located diametrically opposite said second member andoperable" to position said enclosure and transducer unit.

9. The impulse generator of claim 5, in which said resilient member is a helical spring.

10. The impulse generator of claim 6, inwhich said resilient member isl a helical spring, and said adjustable element is a threaded screw. g V

11. The impulse generator of claim 1, in which said of claim 3, in which said.

of said first member and;

resilient members are; helical springs and saidadjustableelement's-are threaded screws.

H 12". The impulse generator of claim 5, further includ ing a set-screw associated with said resilient member to secure said enclosure and transducer unit together with said housing.-

' 13.3Thefimpulsegenerator of claim. 10, further including asct-screwcentrally through said helical spring :to secure said enclosure and transducer unit in conjunc tion with said threaded screw.

14. The impulse generator ofclaim 11, further includ-- ing-a set-screw centrally through each of said helicalsprings to secure said enclosure and transducer unit in conjunction with said threaded screws. v

1 5, The impulse generator of claim 12,,in which saidlocking means includes a saidset s crew. I v v v l6. The impulse generator of claim 14, in which said locking means includes locking screws; settable against said set-screws and said threaded screws.

1-7. The impulse generator of claim 3, further includinga clamping ring engageable withsaid housing for locking said enclosure therewith.

. 18. The impulse generator of claim 4,- further including a clamping ring engageable with said housing for locking said transducer enclosure therewith across said flange.

19. The impulse generator of claim 8, further includ-i ing -a set-screw centrally through each of said helical springs to secure said transducer unit, and a clamping ringengageable with said housing for locking said transducer enclosure therewith across said; flange.

eluding a clamping ring engageable with said housing for looking said transducer enclosure therewith across said flange.

References Cited in the file of this patent UNITED STATES PATENTS 2,722,608 George etal. Nov. 1, 1955 locking screw settable against 0 The impulse generator of claim 15, furtheriin- 

